Understanding clinical
trial results

It can take many years before the results of a clinical trial are known.

In many trials, researchers will want to know how effective a treatment has been. If the cancer has stopped growing, become smaller or disappeared, it is known as a response. You may hear your doctors talking about a complete response, a partial response or stable disease:

Complete response – all the cancer has disappeared. It is not usually thought of as a cure until there has been no sign of it returning for several years.

Partial response – the cancer has decreased in size by at least 30%.

Stable disease – the cancer has decreased in size by less than 30%.

Other trials look at the long-term side effects of a treatment or how long people live for after their treatment.

You can usually find out the results of your clinical trial by speaking to your specialist.

Reviewed: 30 Sep 2015 Next review: 2018

Why trial results take a long time to be published

It can sometimes take many years to get the results of a trial. This may be because many thousands of people need to take part to show a small but important difference between treatments.

If a trial is looking at how long people live after their cancer treatment, they need to be monitored for many years – often five years, but sometimes 10 years or more. Researchers continue to collect this information during this time. The information is collected from the hospital, national records or a patient’s GP.

Patients’ names are removed so individual people will not be identified in the study results.

Understanding trial results

Researchers need to collect information (called outcomes or endpoints) to help them decide which treatment is most effective and safest.

In a phase 2 trial, the first outcome that researchers look for is how effective the treatment has been in treating the cancer.

In solid tumours (not blood cancers like lymphomas, leukaemias and myelomas), if the cancer has stopped growing, shrunk or disappeared, it’s known as a response.

You may hear your doctors use different phrases to describe your response to treatment, such as a complete or partial response, or stable disease:

A complete response is defined as the disappearance of all of the detectable cancer for at least four weeks. Clearly this is a very good result, but a complete response doesn’t always mean a cure. It takes several years with no sign of the cancer returning (recurrence) before it can be thought of as cured.

A partial response is a decrease in cancer size by at least 30% for at least four weeks, without any signs of growth elsewhere in the body.

Stable disease is when the cancer has shrunk in size, but by less than 30%, and there are no signs of growth elsewhere in the body.

These definitions also help doctors to describe the effects of the drugs on the tumours in a standard way.

Some trials look at long-term outcomes of treatment. In a phase 3 trial, researchers are often looking at how long people live after the treatment (survival). Doctors and researchers monitor whether more people are cured, or live longer, with the new treatment.

Finding out results

The results of most clinical trials will be published in medical journals. However, a final report of a trial may not be published until many years after people were treated. If you don’t read medical journals, you may not get to know the results.

But sometimes they are published in newspapers or discussed on TV or the radio, especially if the results are presented at doctors’ conferences.

Researchers are expected to think about how people taking part in their trial will be told the results. If this isn’t explained to you when you join the trial, ask the research team.

Generally the best way to find out results is to ask your specialist. However, more patients are now being contacted directly when results of trials are available.

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